A cohort of patients infected with human T-cell lymphotropic virus, types I and II (HTLV-I/II) will be constructed and followed through time. At least half of these patients will have dual infection with human immunodeficiency virus (HIV-1). The natural history of single versus dual infection will be assessed through clinical and laboratory studies. This is a prospective study, in which the exposure criteria is HTLV-I/II.